I have a battery operated circuit that is triggered by a mechanical push button. What optical component could I use that when I cover it with my figure it triggers a mosfet. 4.2 v battery.
Want an optical button I guess.

The push button triggers the mosfet which switches a large resistive load. Nice to change the mechanical button to a touch sensor or ir sensor

 

Post a schematic of how the mechanical switch triggers your circuit so we don't have to play 20 questions.

 

Depends to some degree what you want to switch?

 

Depends upon how good a "figure" you have.

 

You may want something along the lines of this



...which was taken from a Lewis Loflin video on Opto circuits which you can watch here....

Good luck

 

You could use a voltage divider consisting of a light dependent resistor (LDR/photocell/photoresistor) and resistor on the gate of the N channel MOSFET.

For more abrupt switching action and/or hysteresis, you could add a comparator.